1. Field of the Invention
The present invention relates to a substrate-type non-reciprocal circuit element and an integrated circuit using the same, and more specifically to a substrate-type non-reciprocal circuit element, such as a circulator and an isolator, suitably used in a high frequency circuit, and an integrated circuit using the same.
2. Description of Related Art
One example of a prior art non-reciprocal circuit element is disclosed in U.S. Pat. No. 5,419,947, the content of which is incorporated by reference in its entirety into this application. Of the non-reciprocal circuit element, one example of the substrate-type non-reciprocal circuit element is shown in FIG. 7 which is a diagrammatic perspective view illustrating a substrate-type circulator, which is one example of a three-terminal circulator.
This substrate-type circulator includes a substrate 1 and a ferrite 2 embedded in the substrate 1. A central electrode pattern 3 is formed on an upper surface of the ferrite 2, and lead-out conductors (signal conductors) 4 are formed on an upper surface (or one principal surface) 1a of the substrate 1 to extend from the central electrode pattern 3 in three different radially-outward directions. A ground electrode 5 is formed on a lower surface (or the other principal surface) of the substrate 1.
This substrate-type circulator is put on a carrier member and is conveyed in that condition, and thereafter mounted on a circuit board. For example, when the substrate-type circulator is connected to a transceiver circuit board (device), the respective lead-out conductors 4, which constitute connection terminals, are connected to corresponding electrodes on the circuit board by means of a wire bonding or another.
In an actual operation, it is an ordinary practice to position a magnet (not shown) above the ferrite 2. Thus, this substrate-type circulator has such a non-reciprocal feature that a signal applied to one lead-out conductor 4 is never returned to the same lead-out conductor 4 but is outputted from another lead-out conductor 4.
Here, if one terminal of the substrate-type circulator is terminated with a matching load, the substrate-type circulator can be converted into a substrate-type non-reciprocal circuit element having a function as an isolator.
For example, the above mentioned substrate-type circulator can be operated as an isolator, if one lead-out conductor 4 is grounded through a reflectionless resistor. In this case, the reflectionless resistor can be obtained by forming a thin film resistor on the substrate 1. In the thin film resistor, however, it is generally difficult to precisely control the resistance, and therefore, the resistance of the thin film resistor is adjusted by a trimming such as a laser trimming.
In the prior art substrate-type circulator, variation of the size inevitably occurs in a manufacturing process, for example, in a process for embedding the ferrite 2 into the substrate 1, and in a process for forming the central electrode pattern 3. As a result, the high frequency characteristics of the circulator varies, and therefore, it was necessary to conduct a sorting with reference to an appearance and an electric characteristics.
In the case of this substrate-type circulator, since the variation of the size gives a large influence to a high frequency characteristics in a very high frequency region such as a millimeter wave band, it is necessary to adopt a reliable characteristic evaluation method for the sorting.
In this very high frequency region, on the other hand, it is not so easy to realize a good electrical connection between the substrate-type circulator before the mounting and a characteristic evaluation machine, and therefore, it is difficult to precisely conduct a large amount of sorting. Even if there is used a test fixture so configured to catch the substrate 1 between a pair of members so as to cause the terminals of the circulator, namely, the lead-out conductors 4 to be pressure-connected to connector terminals, it is difficult to measure a large number of substrate-type circulators in the millimeter wave band with a good repeatability.
In addition, when the lead-out conductors 4 are connected to electrodes of the circuit board by means of the wire bonding, the wiring length becomes as long as about 100 xcexcm to 500 xcexcm because of a mounting margin of the circuit board. Furthermore, because of a restriction in the mounting precision, it is difficult to maintain the length of the wire at a constant value. In the very high frequency region such as the millimeter wave band, therefore, a reflection loss attributable to an inductance of the wire and variation in the inductance of the wire give a large influence to a transmission characteristics, with the result that it was difficult to connect between the transceiver circuit and the substrate-type circulator with a low loss and with a small variation in the loss.
This problem is also true in the case that the substrate-type circulator is used as the isolator.
Furthermore, when the substrate-type circulator is used as the isolator, it is also difficult to surely evaluate the electric characteristics of the isolator in the very high frequency region such as the millimeter wave band, similarly to the circulator. In addition, it was difficult to evaluate and to adjust the thin film resistor.
Therefore, there is a strong demand to perform the evaluation of the electric characteristics and the evaluation and the adjustment of the thin film resistor, before the mounting, by a means having a very simple construction.
Accordingly, it is an object of the present invention to provide a substrate-type non-reciprocal circuit element which has overcome the above mentioned problems of the prior art.
Another object of the present invention is to provide a substrate-type non-reciprocal circuit element, enabling to easily measure the electric characteristics of the substrate-type non-reciprocal circuit element with a high precision and a high repeatability, thereby to easily and precisely perform the sorting before the mounting.
Still another object of the present invention is to provide a substrate-type non-reciprocal circuit element, enabling to electrically connect the substrate-type non-reciprocal circuit element on a circuit board such as a transceiver circuit board, with a small loss and with a small variation in the loss.
A further object of the present invention is to provide an integrated circuit incorporating therein a substrate-type non-reciprocal circuit element.
The above and other objects of the present invention are achieved in accordance with the present invention by a substrate-type non-reciprocal circuit element having a plurality of signal conductors and so configured that a signal inputted through one signal conductor is outputted from another signal conductor, the substrate-type non-reciprocal circuit element comprising a substrate, a ferrite embedded in the substrate, a central electrode formed on the ferrite at one principal surface of the substrate, a plurality of signal conductors formed on the one principal surface of the substrate to extend from the central electrode into a plurality of different outward directions, and a first ground electrode formed on the one principal surface of the substrate, separately from the central electrode and the plurality of signal conductors.
Specifically, the first ground electrode is formed at opposite sides of each of the signal conductors, separately from each of the signal conductors, so as to form a coplanar waveguide between each of the signal conductors and the first ground electrode.
In one embodiment, a reflectionless resistor is located at the side of the one principal surface of the substrate and is connected between one of the signal conductors and the first ground electrode.
Preferably, a second ground electrode is formed on the other principal surface of the substrate and is electrically connected to the first ground electrode. This second ground electrode can be electrically connected to the first ground electrode by a side surface electrode formed on a side surface of the substrate or by through-holes formed to penetrate through the substrate from the first ground electrode to the second ground electrode.
According to another aspect of the present invention, there is provided an integrated circuit comprising an integrated circuit board and the substrate-type non-reciprocal circuit element as mentioned above, the substrate-type non-reciprocal circuit element being electrically connected to the integrated circuit board in a flip chip method.
In one embodiment, the substrate-type non-reciprocal circuit element is accommodated in a recess formed in the integrated circuit board.
In the above mentioned substrate-type non-reciprocal circuit element in accordance with the present invention, since the plurality of signal conductors extending from the central electrode in the plurality of different directions and the first ground electrode are formed on the one principal surface of the substrate, if a probe having a plurality of contacting terminals located in the same plane is used, it is possible to realize a good electrical contact between the probe and the substrate-type non-reciprocal circuit element in a very high frequency region such as the millimeter wave band.
Therefore, the substrate-type non-reciprocal circuit element can be easily electrically connected to a measurement machine, whereby an electrical characteristics can be precisely and easily measured with a good repeatability.
In addition, since the plurality of signal conductors extending from the central electrode in the plurality of different directions and the first ground electrode are formed on one principal surface of the substrate, the substrate-type non-reciprocal circuit element is simple in construction.
Furthermore, in the integrated circuit mentioned above in accordance with the present invention, since the signal conductors and the ground electrode are formed on the same principal surface of the substrate of the substrate-type non-reciprocal circuit element, the signal conductors and the ground electrode of the substrate-type non-reciprocal circuit element can be connected to signal conductors and a ground electrode of a coplanar waveguide formed on the integrated circuit board, respectively, by means of the bumps with an extremely short connection distance. Therefore, when the substrate-type non-reciprocal circuit element is connected to an electric circuit such as the receiver circuit and the transmitter circuit, the transmission loss itself and the variation in the transmission loss can be minimized.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.